The objective of this proposal is to develop a practical flat-panel x-ray imaging detector with programmable gain in order to address the increasing demand for wide dynamic range flat panel detectors in advanced x-ray imaging applications. The proposed detector employs three major components: a structured cesium iodide (CsI) scintillator to convert x-rays to optical photons;an avalanche amorphous selenium (a-Se) photoconductor, HARP (High-gain Avalanche Rushing amorphous Photoconductor), to convert the optical image to charge and provide a programmable gain;and a large area active matrix (AM) thin film transistor (TFT) array to read out the image electronically in real-time. The proposed detector has been named SHARP-AMFPI (Scintillator-HARP Active Matrix Flat-Panel Imager). It is capable of producing x-ray quantum noise limited images at the lowest dose expected for x-ray imaging (0.1 <R), which virtually has only one x-ray photon per pixel. For high dose applications (e.g. radiography) the gain of HARP will be decreased to ensure wide dynamic range without detector saturation. In our previous work we have established the theoretical and experimental feasibility of all components of SHARP-AMFPI using models and small scale imaging prototypes. The goal of the proposed work is to develop a practical large area SHARP-AMFPI detector with a distributed resistive interface layer (RIL) to achieve stable and reliable avalanche gain. Our goal will be achieved through the following three specific aims: (1) Develop large area RIL technology to achieve stable avalanche gain in SHARP-AMFPI;(2) Optimize RIL properties to allow integration of HARP with the TFT array, and achieve the desired surface topology and imaging performance;(3) Demonstrate the superior imaging performance and reliability of a practical large area SHARP- AMFPI. Once these aims are accomplished a new AMFPI ready for clinical translation will be resulted, and permit major advancements in the application of x-ray imaging in multimodality clinical applications. PUBLIC HEALTH RELEVANCE: In the proposed work we will develop the next generation x-ray flat-panel detectors for low dose imaging. It will increase the efficiency of x-ray detection in fluoroscopy by up to 5 times while maintaining the capability for dual mode fluoroscopy/radiography operation by virtue of programmable gain.